1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) device, and more particularly, to an LCD device and a method for manufacturing the same to minimize degradation of perception in a portion where a defect may be generated.
2. Discussion of the Related Art
Demands for various display devices have increased with the development of an information society. Accordingly, many efforts have been made to research and develop various flat display devices such as liquid crystal display (LCD), plasma display panel (PDP), electroluminescent display (ELD), and vacuum fluorescent display (VFD). Some types of flat display devices have already been incorporated as displays for various types of equipment.
Among the various flat display devices, liquid crystal display (LCD) devices have been most widely used because of their excellent picture quality, thin profile, lightness in weight, and low power consumption, thus providing an advantageous substitute for a Cathode Ray Tube (CRT) display. In addition to mobile type LCD devices such as notebook computers, LCD devices have been developed for computer monitors and televisions to receive and display broadcasting signals.
In order to incorporate LCD devices in various fields as a general display, the key to developing LCD devices depends on whether LCD devices can produce a high quality picture, such as high resolution and high luminance with a large-sized screen, while still maintaining lightness in weight, thin profile, and low power consumption.
Hereinafter, a related art LCD device disclosed in Korean Patent Publication No. P2001-0103430, Nov. 23, 2001, which is hereby incorporated by reference for all purposes as if fully set forth herein, will be described with reference to FIG. 1.
FIG. 1 is an exploded perspective view illustrating a related art LCD device.
The Related Art LCD device 10, as shown in FIG. 1, includes first and second substrates 1 and 2 bonded to each other with a gap therebetween, and a liquid crystal layer 3 formed between the first and second substrates 1 and 2 by injection.
In more detail, the first substrate 1 includes a plurality of gate lines 4 arranged along a first direction at fixed intervals and a plurality of data lines 5 arranged along a second direction perpendicular to the first direction at fixed intervals. A plurality of pixel regions P are defined by the gate and data lines 4 and 5, respectively. A plurality of electrodes 6 are arranged within the pixel regions P, A plurality of thin film transistors T are formed at regions where the gate lines 4 cross the data lines 5 and apply data signals of the data lines 5 to the pixel electrodes 6 in accordance with signals applied to the gate lines 4.
The second substrate 2 may further include black matrix layers 7 that block light from portions except the pixel regions P, R/G/B color filter layers 8 formed to correspond to the pixel regions, for displaying various colors, and a common electrode 9 for producing the image on the color filter layers 8.
In the aforementioned related art LCD device, the liquid crystal layer 3 is formed between the first and second substrates 1 and 2, wherein liquid crystal molecules of the liquid crystal layer 3 are driven by an electric field generated between the pixel electrodes 6 and the common electrode 9. Light irradiated through the liquid crystal layer 3 may be controlled by the alignment direction of the liquid crystal molecules 3, thereby displaying an image. This type of LCD device is referred to as a twisted nematic (TN) mode LCD device.
In addition, an in-plane switching (IPS) mode LCD device has been developed. In the IPS mode LCD device, a pixel electrode and a common electrode are formed in a pixel region of a first substrate in parallel to each other at a fixed interval, so that an IPS mode electric field (horizontal electric field) occurs between the pixel electrode and the common electrode, thereby aligning a liquid crystal layer according to the IPS mode electric field.
Hereinafter, a point defect that may be observed in the related art LCD device will be described.
FIG. 2 is a plane view illustrating a point defect generated by foreign materials under a black state in a general LCD device, and FIG. 3 is a sectional view illustrating the point defect of FIG. 2 and its adjacent pixel.
As shown in FIGS. 2 and 3, a related art TN mode LCD device includes first and second substrates 1 and 2 facing each other, pixel electrodes 6 formed for every pixel region of the first substrate 1, and a common electrode 9 formed on an entire surface of the second substrate 2. Also, black matrix layers 7 are formed on a non-pixel region of the second substrate 2, and color filter layers 8 are formed on a pixel region of the second substrate 2.
In the aforementioned TN mode LCD device, if conductive foreign materials 21 remain on a predetermined portion of the pixel electrodes 6, they join the common electrode 9 of the second substrate 2, whereby the pixel electrodes 6 on the first substrate 1 are electrically connected with the common electrode 9 above the second substrate 2. Such conductive foreign materials 21 may be particles remaining on the first substrate 1 or the second substrate 2 as remaining residues resulting from an etching process of a metal or transparent electrode that do not get removed even after a cleaning process. Such conductive foreign materials 21 may also be particles generated in the first substrate 1 or the second substrate 2 during various other process steps. If the foreign materials 21 remain in the portion where the pixel electrodes 6 are formed, they allow the common electrode 9 to be electrically connected with the pixel electrodes 6. As a result, a problem occurs because the corresponding portion of the pixel electrodes 6 and the common electrode 9 is always in a shorted state due to the foreign materials 21.
In this case, in the TN mode LCD device driven in a normally white mode, the corresponding portion of the pixel electrodes 6 always shows a white state regardless of a voltage applied to the pixel electrodes 6. For this reason, a white point defect is observed during a black state where the voltage is applied. In addition, the white point defect may be generated by electrical short or burnout.
Meanwhile, even if the foreign materials 21 are not conductive, or even if the LCD device is not driven in a TN mode, the white point defect may be generated. For example, when an alignment layer is rubbed, a portion where foreign materials 21 remain may not be aligned well unlike other portions. This portion is observed as a portion where light leakage occurs. As described above, in the related art LCD device, light leakage may be generated by an uneven alignment region. Such light leakage causes the white point defect by degrading light transmittance of the liquid crystal layer 3.
Generally, in the case of a high gray (white state) level, a dark portion observed because of light leakage is referred to as a blind spot. In the case of a low gray (black state) level, a bright portion observed because of light leakage is referred to as a white point defect. Human eyes are more susceptible to the white point defect of a relatively dark state than the “blind” white point defect of a bright state. Accordingly, in determining whether the LCD panel has a defect, stricter standards are used to test whether the white point defect is generated. It is thus necessary to provide a method for minimizing defect ratio generated by a white point defect in an LCD panel.
If a defect occurs in each thin film of the first and second substrates 1 and 2, according to the related art LCD device, either a rework process or a repair process is performed. The rework process is performed by way of a deposition process of a corresponding thin film, while the repair process is performed using a laser.
However, the foreign materials 21 may still remain between the first and second substrates 1 and 2, as shown in FIGS. 2 and 3, in spite of the rework process or the repair process. If the first and second substrates are bonded to each other and the foreign materials 21 remain, it is impossible to perform the rework process. Also, it is not easy to perform the repair process. That is, the laser repair process may fail even when burnout occurs.
The aforementioned related art LCD device has several problems.
If the foreign materials remain between the upper and lower substrates in the LCD panel, the point defect is generated by the foreign materials, wherein the point defect is varied depending on modes of the LCD device. If the foreign materials remain on each thin film of the upper and lower substrates during an array process, before the bonding process of the substrates, the rework process or the repair process may be performed to remove the foreign materials. The upper and lower substrates of the LCD panel may be bonded to each other while foreign materials remain during a cleaning process which could lead to the point defect.